An image sensor is a device that converts an optical signal into an electric signal. The image sensor may include a photoelectric conversion unit which senses light and converts the sensed light into an electric signal, and a logic circuit unit which stores the electric signal as data. In order to elevate optical sensitivity, the image sensor may further include a microlens, which may change the path of light to travel to the photoelectric conversion unit to condense light.
In a conventional image sensor, a multilayered interconnection layer may be disposed on a substrate having a photoelectric conversion unit, and a color filter layer and a microlens may be disposed on the interconnection layer. Thus, it may be difficult to ensure a sufficient focal length due to a long distance between the color filter layer and the photoelectric conversion unit, and the scattered reflection and covering of incident light by the interconnection layer may lead to a decline in the light reception efficiency of the photoelectric conversion unit.
In order to improve the foregoing problems, a back-illuminated image sensor has been proposed. In the back-illuminated image sensor, a color filter layer and a microlens may be disposed on a rear surface of a substrate to reduce a distance between a photoelectric conversion unit and the color filter layer and increase the light reception efficiency of light incident on the photoelectric conversion unit.
FIG. 1 is a cross-sectional view of a conventional back-illuminated image sensor. Further, FIG. 1 illustrates a portion of a pixel region of the image sensor excluding a circuit region disposed around the pixel region.
Referring to FIG. 1, a plurality of photodiodes 23 may be disposed in a substrate 20, and an interlayer dielectric layer 24 may be disposed on a first surface of the substrate 20. A multilayered interconnection layer 25, which includes a plurality of interconnection lines, may be disposed in the interlayer dielectric layer 24.
A plurality of color filters 27 may be provided on a second surface of the substrate 20, which may oppose the first surface, and a microlens 29 may be disposed on the color filters 27.
While light condensed by the microlens 29 is passing through the color filters 27, red (R), green (G), or blue (B) light may be selected and incident on the substrate 20. Due to a difference in extinction coefficient according to wavelength, B light having a wavelength near 450 nm and G light having a wavelength near 550 nm may be absorbed in the photodiode 23, while R light having a wavelength near 650 nm may reach an interface between the substrate 20 and the interlayer dielectric layer 24. Thus, when light reflected by the interface between the substrate 20 and the interlayer dielectric layer 24 is incident on an adjacent photodiode 23, undesired ghost images may result.